An uninterruptible power supply (system) configured to continue supply of power to equipment connected therewith for a fixed period of time without power failure even if the input power source fails is used widely.
For example, it is common for a computer system to receive power supply from a commercial power source. In the computer system when the power source fails, even if instantaneously, a large-scale malfunction occurs, and therefore, an uninterruptible power system is used to prevent an instantaneous voltage drop or power failure even if the commercial power source with which the computer system is connected fails. In addition to the computer system, there exist various facilities and equipment for which even an instantaneous power failure will cause a large-scale malfunction, such as hospitals and plants, and medical equipment, control equipment, and sensors, used in such facilities. Generally, such facilities and equipment comprise an uninterruptible power system. Hereinafter, explanation is given using an Internet Data Center (IDC) as an example, however, the following explanation is not limited to this. The Internet Data Center (IDC) has a plurality of processor units and a computer system that performs processing in parallel.
The uninterruptible power system stores power and maintains supply of power to equipment by supplying stored power to the equipment when supply of power is cut off. To store power, a secondary battery or an electric double layer capacitor is used, however, either requires DC power. Hereinafter, the secondary battery and the electric double capacitor are generally referred to as a secondary battery. Further, the whole of the uninterruptible power supply is sometimes referred to as UPS (Uninterruptible Power Supply), however, the portion that stores power is sometimes called UPS. In the following explanation, a power storage device that stores power is referred to as UPS.
The uninterruptible power system includes an alternating-current (AC) power supply type and a direct-current (DC) power supply type. When the uninterruptible power system is used for the power source of the whole of a facility, an AC power supply uninterruptible power system is used in view of distribution of power etc. within the facility. However, when the uninterruptible power system is used for the power source of the whole of the facility, the capacity and weight of the system become very large. For example, when the uninterruptible power system is used for the power source of the whole of the Internet data center (IDC), the uninterruptible power system is provided on the floor corresponding to one story and the computer system is provided on the next upper or lower floor.
In the AC power supply uninterruptible power system, the AC commercial power is once converted into DC power and to the output of the DC power, UPS is connected. Then, the output of the DC power is converted into AC power and supplied to each part in the form of AC power. Equipment (processor unit) to which AC power is supplied operates on DC current, and therefore, the supplied AC power is converted into DC power again and supplied to the equipment (processor unit). Consequently, when the AC power supply uninterruptible power system is used in the Internet data center (IDC), conversion is performed three times, that is, AC/DC conversion, DC/AC conversion, and AC/DC conversion. Because of this, for the AC power supply, there has been such a problem that power loss accompanying conversion is large and efficiency is low. Further, there has been a problem that the size of UPS is large.
Equipment to which AC power is supplied is referred to as AC equipment and equipment to which DC power is supplied and which operates on DC power is referred to as DC equipment. AC equipment having DC system unit inside thereof has an AC/DC converter to which AC power is supplied from outside and which is configured to convert AC power into DC power inside thereof. The DC system unit provided inside of the AC equipment is sometimes referred to as DC equipment.
For power saving and a reduction in environmental load of the Internet data center (IDC), development of the technique relating to DC power supply and power load leveling is promoted.
In the DC power supply, AC commercial power is converted into DC power, UPS is connected to the output of the DC power, and the DC power is supplied to the equipment (processor unit). UPS in this case is referred to as DC-UPS. In this case, conversion is performed once and the loss of power accompanying conversion can be reduced, and therefore, it is possible to make an attempt to save energy. However, from a converter from AC power into DC power, DC power is supplied to each piece of DC equipment, and therefore, the voltage drop and the loss of power accompanying distribution of power are problems.
On the other hand, the power load leveling is the technique to compensate for and suppress fluctuations in system power and power consumption by charging and discharging the power storage device by also providing a large capacity power storage device in order to match the system power originating from recycled energy and atomic power, the environmental load of which is low but the output control of which is difficult, with fluctuations in power consumption of the equipment.
In order to implement these DC power supply and power load leveling technique, there is a DC power supply uninterruptible power supply (DC-UPS) in which a power storage device is installed in the DC system unit inside of the AC equipment. DC-UPS is charged by DC power from the AC/DC converter provided in the AC equipment and the discharged power from DC-UPS is supplied to the DC system unit within the equipment as DC power without conversion. According to this power supply system, it is possible to implement DC power supply inside of large-sized information equipment without converting power to be supplied to the whole of IDC into DC power, and therefore, power saving is enabled. Further, according to this power supply system, DC-UPS has only the secondary battery and a charge/discharge control circuit and the DC/AC conversion circuit is not provided and by additionally providing a power storage device in the space once used for the DC/AC conversion circuit, it is made possible to implement UPS with a power capacity by which it is possible to back up large-sized information equipment and to level a power load.
As described above, in the case of AC power supply, the AC power supplied to the facility is supplied once to AC equipment via the AC power supply uninterruptible power supply (AC-UPS) and is subjected to AC/DC conversion inside of the AC equipment (built-in power source unit). The DC power is supplied to the DC system unit inside of the equipment after further converting into DC power of a desired voltage by DC/DC conversion in correspondence to the equipment drive voltage.
On the other hand, in the case of DC power supply, the AC power supplied to the facility is supplied directly to the AC equipment and connected to DC-UPS by drawing the DC power subjected to AC/DC conversion inside of the AC equipment (built-in power source unit). The DC output of DC-UPS is supplied to the DC/DC converter and after converted into DC power of a desired voltage in correspondence to the drive voltage inside of the equipment, is supplied to the DC system unit inside of the equipment.